In internal combustion engines, with increasing frequency, cases have become known in which relatively large quantities of water have passed into the air intake duct. Air mass sensors usually based on hot-film manometry are normally arranged in the intake manifold in the air intake duct. In these air mass sensors, considerable distortion of the measuring signal or even failure of the sensor occurs in the event of the sensor element coming into contact with water.
The actual air mass sensors are accommodated in an air flow passage of an air mass sensor arrangement. EP 0 908 704 A1 shows an example of an air mass sensor arrangement which is inserted in an intake manifold of an internal combustion engine and in which the air flow passage in the sensor arrangement runs essentially perpendicularly to the air flow direction in the intake manifold, a factor which may be regarded as a first step in avoiding contact of the sensor element with water; however, this step is not nearly adequate. The air inlet opening of the sensor arrangement is oriented perpendicularly to the air flow direction in the intake manifold and is designed to be of relatively large area in order to even out flow fluctuations, which would distort the sensor signal. However, water is increasingly caught by the large-area inlet opening, a factor which again modifies the effect of the curved direction of the flow passage.
A device with an air intake manifold and an air mass sensor arrangement inserted radially therein, in which device a shielding body is arranged upstream of the inlet opening of the air mass sensor arrangement, can be gathered from the product specification of an air mass sensor from Pierburg AG, which according to the history listed there is supposed to be resistant to water and particles. The shielding body, on the one hand, covers the inlet opening, so that no water particles can pass directly into the inlet opening, and, on the other hand, appears to be of streamlined design, so that the air flow nonetheless reaches the inlet opening. It is at the same time designed to be rectilinear in the flow direction transversely to the curved profile of its surface and is arranged in the intake manifold in such a way that the direction of this rectilinear profile is parallel to the insertion direction of the air mass sensor arrangement.
According to the description with regard to a diagram on page 4 of the product specification, a water flow of 2.5 ml/min is taken as a basis, which can easily be coped with by the device shown. However, water flows of over 200 ml/min often occur in practice, and the device shown would probably hardly be able to cope with these water flows, since a large number of water particle ricochets can pass into the inlet opening of the air mass sensor arrangement.
DE 10015918A1 discloses a device for determining at least one parameter of a medium flowing in a line, this device having an air pipe into which a mass sensor arrangement is inserted radially. In the flow direction upstream of the measuring arrangement, a deflecting grid is arranged in the intake manifold, this deflecting grid directing the flowing air onto a baffle mound which is integrally formed in the interior of the intake manifold and is arranged between the grid and the measuring arrangement.
DE19632198C1 discloses a device for measuring the mass of a flowing medium, this device having an air flow pipe and a measuring arrangement which is inserted radially into the air flow pipe. Arranged upstream of the measuring arrangement is a baffle body whose longitudinal extent runs in a direction parallel to the insertion direction of the measuring arrangement in the air pipe.
DE1001642A1 discloses a device for determining at least one parameter of a flowing medium, this device having an air flow pipe in which a measuring arrangement is inserted in the radial direction. Furthermore, this device has a deflecting body which is arranged upstream in the flow direction and whose longitudinal extent runs parallel to the insertion direction of the sensor arrangement in the intake manifold. The task of the baffle body is to produce flow separation at sharp-edged corners. Arranged between the disturbance body and the measuring arrangement is a guide body which is intended to feed partial air flows to the measuring arrangement in a defined manner.